1. Technical Field
The present invention relates to rotors and rotating electric machines that include those rotors and are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of Related Art
There have been known rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators. Those rotating electric machines generally include a rotating shaft, a rotor fixed on the rotating shaft so as to be rotatable together with the rotating shaft, and a stator disposed in radial opposition to the rotor.
Moreover, there also have been known, for example from Japanese Patent Application Publication No. JP2011-259689A, methods of fastening a rotor core of the rotor to the rotating shaft. Those fastening methods include: (a) a method of fitting keys (or protrusions) formed in one of the rotor core and the rotating shaft into keyways (or recesses) formed in the other of the rotor core and the rotating shaft; (b) a method of performing a knurling process on contact surfaces of the rotor core and the rotating shaft; and (c) a method of press-fitting the rotor core onto the rotating shaft.
However, in the case of using the fastening method (a), there exist circumferential backlashes between the keys and the wall surfaces of the keyways. Consequently, when the rotor and the rotating shaft together rotate at a high speed, the rotor may vibrate due to the backlashes, resulting in torque variation. Moreover, due to the backlashes, the characteristics of the rotating electric machine and an inverter connected to the machine may be deviated from their respective initial set values.
In the case of using the fastening method (b), when the rotor and the rotating shaft together rotate at a high speed, backlashes may be created between the contact surfaces of the rotor core and the rotating shaft due to the difference between the centrifugal force acting on the rotor and the centrifugal force acting on the rotating shaft. Consequently, the rotor may vibrate due to the created backlashes, resulting in torque variation. In addition, in this case, the created backlashes will disappear when the rotor and the rotating shaft come to rotate at a low speed or be stopped.
In the case of using the fastening method (c), the interference between the rotor core and the rotating shaft is generally set so as to be equal to zero when the rotor and the rotating shaft together rotate at a maximum speed. Accordingly, during the process of press-fitting the rotor core onto the rotating shaft, the interference between the rotor core and the rotating shaft will be largest, causing high press-fit stress to be induced in the rotor core. Consequently, the rotor core may be deformed due to the high press-fit stress, thereby changing a predetermined air gap between the rotor core and the stator of the rotating electric machine which is disposed in radial opposition to the rotor core.